The present invention relates to a generated-voltage regulator mounted on an automobile. As an example of a generated-voltage regulator mounted on an automobile, there is a charge indicator described in Japanese Patent application: JP-A 62-81939, incorporated herein by reference.
In the charge indicator described in JP-A 62-81939, a key switch, a charge lamp and a bipolar transistor for lighting or putting on the charge lamp are connected in series to a battery. When the key switch is turned on, the level of an input voltage of a voltage detecting unit is turned to a high ("H") level so that the operation of the voltage regulator starts.
In a normal state, the lamp-lighting transistor is in an off state, so that the charge lamp is not lighted. When, for example, a failure such as breaking of a field winding occurs in a generator, the lamp-lighting transistor is turned on so that the charge lamp is lighted. Since the level of the input voltage of the voltage detecting means is lowered when the lamp-lighting transistor is turned on, it might be predicted that the voltage detecting section may make a misjudgment that the key switch is turned off. In fact, however, the voltage detecting section never makes such a misjudgment, because the collector-emitter voltage of the lamp-lighting transistor upon turn-on is sufficiently higher than the level of the input voltage of the voltage detecting section when the key switch is off.
As another example similar to the aforesaid generated-voltage regulator, there is a charger described in Japanese patent application JP-A 57-116552, also incorporated herein by reference, in which the charging operation of a battery is controlled, depending on the on/off operation of a MOS FET connected to the battery.
As a further example, similar to the aforesaid generated-voltage regulator, there is a field voltage regulator for regulating a field voltage in an AC generator, as described in Japanese patent application JP-A 1-99500, which is also incorporated herein by reference. In this voltage regulator, a field current is regulated, depending on the on/off operation of a field-effect transistor connected in series to a field coil.
In the charge indicator described in JP-A 62-81939, the collector-emitter voltage of the charge lamp-lighting transistor upon turn-on is considered to be sufficiently high as described above. However, if the ambient temperature in the lamp-lighting transistor changes, or if the resistance increases in the charge lamp, wiring in the vicinity of the lamp-lighting transistor, or the like increases, then the collector-emitter voltage of the transistor upon turn-on of the transistor is lowered. Accordingly, in the conventional apparatus, when the charge-lamp lighting transistor is turned on, the operation of the voltage regulator may stop, because of misjudgment that the key switch is turned off.
Further, in the conventional apparatus, a bipolar transistor is used as the charge-lamp lighting transistor. Because the bipolar transistor has a large size and generates a large heating value upon operation, this is a barrier to reduction in size and weight or the voltage regulator.
It may be therefore thought of that a power MOS FET is used as a power transistor for lighting the charge lamp. However, in its on state, the drain-source voltage of the power MOS FET takes a low value, so that it is difficult to be discriminated from the voltage level in the case where the key switch is off. Accordingly, the power MOS FET cannot be employed as the power transistor for lighting the charge lamp, and it is difficult to attain reduction in size and weight of the voltage regulator.
Further, there is a requirement for multiple functions of the voltage regulator, such as a function for interlocking the controlling operation of the voltage regulator with the controlling operation of another controller or the like mounted on the same automobile. To satisfy this requirement, it may be thought of that a digital circuit is used in the voltage regulator for the purpose of integration. However, if a digital circuit is used in the voltage regulator, then a reset signal generating section is required separately, for performing initialization at the time of the starting-up of the voltage regulator. Accordingly, though multiple functions can be achieved, reduction in size and weight is obstructed.
An object of the present invention, therefore, is to provide a generated-voltage regulator for an automobile, in which the on state of a key switch can be detected securely regardless of the on/off operation of a charge lamp lighting transistor.
Another object of the present invention is to provide a generated-voltage regulator for an automobile, in which reduction in size and weight can be achieved.